Waste disposal process

Abstract

A method of disposing hazardous industrial solid waste, preferably mill tailings, which comprises treating the waste to form a paste and pumping the paste to an underwater paste deposit site in a water saturated area, said area providing permanent water cover for the paste and means for controlling the rate of release of contaminants from the paste into the environment, the paste being pumpable and not readily mixable with ambient water at the deposit site.

What is claimed is: 
     
       1. A method of disposing hazardous industrial solid waste which comprises: a) treating the waste to form a pumpable paste having hydraulic properties of a Bingham fluid;   b) pumping the paste to a paste deposit site in a water saturated area, the paste deposit site having a bottom and comprising a body of standing water;   c) depositing the paste at a location above the bottom of the paste deposit site and under the standing water;   d) said water saturated area providing permanent water cover for the paste;   e) said paste being not readily mixable with the standing water at said deposit site, and said paste further providing control of release of contaminants into the environment.   
     
     
       2. The method of claim 1 wherein the step of treating the waste comprises treating mill tailings. 
     
     
       3. The method of claim 2 wherein the step of treating the mill tailings comprises neutralizing leached ground ore to produce neutralized tailings prior to forming the paste. 
     
     
       4. The method of claim 2 wherein the step of treating the mill tailings comprises treating radioactive mill tailings. 
     
     
       5. The method of claim 2 wherein the step of treating the mill tailings comprises treating mill tailings that contain sulphide minerals. 
     
     
       6. The method of claim 2 wherein the step of treating the waste comprises forming a paste comprising solids and liquid fractions, the solids fraction being, in at least 15% by weight of the solids fraction, particles less than 20 μm in diameter and the liquid fraction being adjusted to provide, when mixed with the solids fraction, a paste density compatible with pumping. 
     
     
       7. The method of claim 2 wherein the step of pumping comprises pumping the paste to a deposit site which is an excavation under the water table. 
     
     
       8. The method of claim 2 further comprising the step of adding a binding agent to the paste prior to the paste being deposited in the deposit site such that the paste will become a hardened mass after deposit in the deposit site. 
     
     
       9. The method of claim 8 wherein the step of adding a binding agent comprises adding portland cement. 
     
     
       10. The method of claim 2 further comprising the step of adding clay to the paste, prior to the paste being deposited in the deposit site, in sufficient quantity to act as a heavy ion contaminant barrier. 
     
     
       11. The method of claim 2 wherein the step of treating the waste comprises forming a paste having a water permeability of 10 -6  cm/sec or less. 
     
     
       12. The method of claim 4 further comprising the step of capping the storage area after completing deposit of the paste. 
     
     
       13. A method of disposing mill tailings comprising: a) treating the mill tailings to form a pumpable paste having properties of a Bingham fluid, the paste having a solids fraction with at least 15% by weight of particles less than 20 μm in diameter;   b) pumping the paste to a paste deposit site comprising an excavation under the water table in a water saturated area, the excavation having a bottom and the deposit site comprising a body of standing water;   c) depositing the paste at a location above the bottom of the excavation and under the standing water;   d) said water saturated area providing permanent water cover for the paste;   e) said paste being not readily mixable with the standing water at the deposit site, and further providing control of release of contaminants into the environment by having a water permeability of 10 -6  cm/sec or less.   
     
     
       14. The method of claim 13 wherein the step of treating the mill tailings to form a pumpable paste comprises using high density thickener technology. 
     
     
       15. The method of claim 13 where the step of depositing the paste comprises pumping the paste through a pipeline having a discharge end which is immersed into previously deposited paste, producing positive displacement of paste as pumping proceeds.